The present invention relates to tunable fiber optic connectors for use in an optical fiber signal transmission system, and to methods for assembling such fiber optic connectors.
Fiber optic cables are used in the telecommunication industry to transmit light signals in high-speed data and communication systems. A standard fiber optic cable includes a fiber with an inner light transmitting optical core. Surrounding the fiber is an outer protective casing.
A fiber terminates at a fiber optic connector. Connectors are frequently used to non-permanently connect and disconnect optical elements in a fiber optic transmission system. There are many different fiber optic connector types. Some of the more common connectors are FC and SC connectors. Other types of connectors include ST and D4-type connectors.
A typical SC fiber optic connector includes a housing having a front end positioned opposite from a rear end. The front end of the SC connector housing is commonly configured to be inserted within an adapter. An example adapter is shown in U.S. Pat. No. 5,317,663, assigned to ADC Telecommunications, Inc. The SC connector typically further includes a ferrule that is positioned within the front and rear ends of the housing, and adjacent the front end. The ferrule is axially moveable relative to the housing, and is spring biased toward the front of the connector. The fiber optic cable has an end that is stripped. The stripped end includes a bare fiber that extends into the connector and through the ferrule.
A connector, such as the connector described above, is mated to another connector within an adapter like the adapter of U.S. Pat. No. 5,317,663. A first connector is received within the front portion of the adapter, and a second fiber is received within the rear portion of the adapter. When two connectors are fully received within an adapter, the ferrules (and hence the fibers internal to the ferrule) contact or are in close proximity to each other to provide for signal transmission between the fibers. Another connector and mating adapter is shown in U.S. Pat. No. 6,142,676, assigned to ADC Telecommunications, Inc.
Signal losses within a system often occur within the connection between two optical fiber cores. Due to manufacturing tolerances of the ferrule outer diameter to inner diameter concentricity, ferrule inner diameter hole size and fiber outer diameter, and fiber core to fiber outer diameter concentricity, when the fiber is inserted into the ferrule the core of a fiber may not and typically does not end up perfectly centered relative to the ferrule outer diameter. If one or both of the fibers are off center, when they are connected within an adapter, the fibers will not be aligned and thus there will be a signal loss when the signal is transmitted between the two fibers. It is therefore desirable to tune a connector to minimize this signal loss. Tuning can be accomplished by measuring signal characteristics through the connector and/or examining physical properties of the connector, and then determining the optimal position of the ferrule and fiber in the connector.
The present invention concerns tunable fiber optic connectors including a spring biased ferrule and hub assembly within the connector. Tuning can be accomplished by partially assembling the connector and pressing the ferrule back into the connector so that an anti-rotation portion of the hub clears an anti-rotation seat of the connector. In this position, the ferrule can be rotated about a connector axis to the desired rotational alignment that minimizes signal loss. The ferrule can then be released, allowing the anti-rotation portion of the hub to re-engage the anti-rotation seat, thereby preventing further rotation that may cause the connector to become un-tuned. The connector is then fully assembled so that the ferrule cannot be inadvertently pushed back into the connector and turned. In addition, stresses placed on the cable and optic fiber cannot cause the attached hub and ferrule to be pulled back into the connector and turned to become un-tuned through rotation of the ferrule. The pulling stresses are especially problematic for small connectors, such as 0.900-millimeter connectors, wherein the cable is without reinforcing strength members.
One aspect of the invention relates to a fiber optic connector including an optical fiber, a ferrule mounted to the optical fiber, a hub retainably engaging the ferrule, wherein the hub includes an elongated rear portion coupled to an anti-rotation portion, a rear housing having an external surface and a bore for receiving the optical fiber, a front housing having an internal surface for receiving and engaging the external surface of the rear housing, having an anti-rotation seat configured to engage the anti-rotation portion of the hub, and defining a cavity coupled to the anti-rotation seat; and a spring captured between the anti-rotation portion of the hub and the rear housing to bias the anti-rotation portion of the hub into the anti-rotation seat of the front housing. A length of the elongated rear portion of the hub is sized so that: (1) the anti-rotation portion of the hub can be pushed completely into the cavity and rotated to tune the connector when the rear housing is partially inserted into the front housing; and (2) an end of the elongated rear portion of the hub abuts the rear housing so that the anti-rotation portion of the hub cannot be completely pushed back into the cavity and rotated when the rear housing is completely engaged with the front housing.
Another aspect of the invention relates to a fiber optic connector comprising a ferrule and hub assembly including an inner bore defining a connector axis and sized for receipt of an optical fiber, a front end defining an end face, an opposite rear end, and an anti-rotation portion disposed between the front and rear ends, a front housing having an anti-rotation seat engageable with the anti-rotation portion of the ferrule and hub assembly in a plurality of positions about the connector axis, a rear housing mountable to the front housing in a first, partially assembled position and a second, fully assembled position, the partially assembled and fully assembled positions defining different relative positions along the connector axis, the front and rear housings defining a chamber for receipt of the ferrule and hub assembly, and a spring within the chamber for biasing the ferrule and hub assembly away from the rear housing. The ferrule and hub assembly is moveable within the chamber along the connector axis against the spring bias when the front and rear housings are in the partially assembled position so that the anti-rotation seat is disengaged from the anti-rotation portion, wherein the ferrule and hub assembly can be rotated about the connector axis relative to the front and rear housings, and the ferrule and hub assembly, when the front and rear housings are in the fully assembled position, engages the rear housing when moved within the chamber along the connector axis, thereby preventing the anti-rotation seat from disengaging from the anti-rotation portion.
Yet another aspect of the invention relates to a fiber optic connector including an optical fiber, a ferrule mounted to the optical fiber, a hub retainably engaging the ferrule, wherein the hub includes an cylindrical rear portion coupled to an anti-rotation portion, a rear housing having an engagement surface and a bore for receiving the optical fiber, a front housing having an engagement surface for receiving and engaging the engagement surface of the rear housing and having an anti-rotation seat configured to engage the anti-rotation portion of the hub; and a spring captured between the anti-rotation portion of the hub and the rear housing to bias the anti-rotation portion of the hub into the anti-rotation seat of the front housing. The front and rear housings together define a cavity having a longitudinal length extending along a connector axis so that: (1) when the rear housing is partially inserted into the front housing, the longitudinal length of the cavity is of sufficient length to allow the anti-rotation portion of the hub to be pushed completely into the cavity and rotated to tune the connector; and (2) when the rear housing is fully inserted into the front housing, the longitudinal length of the cavity is not of sufficient length to allow the anti-rotation portion of the hub to be pushed completely into the cavity and rotated to tune the connector.
Another aspect of the invention relates to a method for tuning a fiber optic connector including steps of: providing a ferrule with a hub retainably engaging the ferrule, the hub including an anti-rotation portion; providing a front housing including a bore with an engagement surface, an anti-rotation seat, and defining a cavity; providing a rear housing including a bore with an engagement surface; inserting the bore of the rear housing partially into the bore of the front housing; pushing the hub into the cavity so that the anti-rotation portion clears the anti-rotation seat of the front housing; rotating the ferrule and the hub to tune the connector; releasing the hub so that the anti-rotation portion re-engages the anti-rotation seat of the front housing; and pushing the rear housing further into the front housing until the rear and front housing are fully engaged.
Another aspect of the invention relates to a method for tuning a fiber optic connector including steps of: providing a fiber held by a ferrule with a hub retainably engaging the ferrule, the hub extending for a length and including a rear end, the connector including front and rear housings engageable with one another, wherein a length of the hub is such that the rear end abuts the rear housing of the connector when the rear housing is fully engaged with the front housing and the ferrule and hub are pushed back towards the rear housing; inserting the rear housing partially into the front housing; pushing the ferrule back towards the rear housing; rotating the ferrule and hub to tune the connector; and pushing the rear housing further into the front housing until the rear housing completely engages the front housing and thereby prevents further rotation of the ferrule and the hub.
Yet another aspect of the invention relates to a method for tuning a fiber optic connector, the method comprising steps of: providing a fiber held by a ferrule with a hub retainably engaging the ferrule, the hub extending for a length and including a rear end, the connector including front and rear housings engageable with one another, wherein a length of the hub is such that the rear end abuts the rear housing of the connector when the rear housing is fully engaged with the front housing and the ferrule and hub are pushed back towards the rear housing; inserting the rear housing partially into the front housing; measuring alignment of the fiber in the ferrule; and pushing the rear housing further into the front housing until the rear housing completely engages the front housing and thereby prevents further rotation of the ferrule and the hub.